The present invention, in some embodiments thereof, relates to compositions and methods for diagnosing and treating diabetes.
The transition of soluble peptides and proteins into highly-ordered amyloid structures is associated with major human disorders including Alzheimer's disease (AD), Parkinson's disease, Prion and Type II Diabetes (T2D). While amyloid fibrils were previously considered as the main pathological elements that facilitate the tissue degeneration observed in amyloid-related disorders, there is an increased body of evidence which suggest a key role for early soluble oligomeric assemblies in the process of cytotoxicity and cell death. A comprehensive postmortem study of AD-associated β-amyloid polypeptide (Aβ) aggregation showed poor correlation between amyloid plaque burden and cognitive functions in elderly population. This lead to the reexamination of the amyloid hypothesis regarding fibrils as the major toxic species in amyloid-associated diseases. Since this early work, a number of studies provided evidence that Aβ oligomers are in fact significantly more cytotoxic than mature fibrils. Moreover the intracranial reintroduction of purified soluble oligomer into the brain of normal rodents resulted in severe memory impairment. Revolutionary work has shown that it is possible to generate soluble toxic oligomeric forms of Aβ 1-42 in vitro [Lambert, M. P. et al. Proc. Natl. Acad. Sci. USA. 95, 6448-6453, (1998); Barghorn, S. et al. J. Neurochem. 95, 834-847, (2005). Braghorn et al. also demonstrated that although these assemblies were formed in vitro under relatively harsh conditions similar epitopes were also observed in vivo in AD patient's brains and in amyloid precursor protein transgenic mice [J. Neurochem. 95, 834-847, (2005)]. These epitopes are currently being used for the development of immunological treatment of AD.
In addition, several proteins that are not associated with any known disease can form oligomers-like structures in vitro [Caughey, B. & Lansbury, P. T. Annu. Rev. Neurosci. 26, 267-298, (2003)]. The observation that these newly formed structures exhibit toxicity similar to amyloid oligomers, suggest a much wider mechanism of toxicity not related to amyloid formation. Amyloid oligomers specifically increase lipid bilayer conductance regardless of the sequence, whereas fibrils and soluble low molecular weight species have no observable effect on membranes [Bucciantini, M. et al. J. Biol. Chem. 279, 31374-31382, (2004)].
The islet amyloid polypeptide (IAPP) is a 37 amino acid peptide hormone, packaged and secreted with insulin by pancreatic β-cells in secretory granules. Under normal conditions IAPP is released into the blood circulation and excreted via the renal system. IAPP is part of the endocrine system and contributes to glycemic control. This peptide is highly conserved between species, implying a functional significance. Type 2 Diabetes (T2D) is characterized by a disruption of insulin secretion from islet Langerhans cells and decreased insulin sensitivity of peripheral tissue. The first description of amyloid deposits in pancreatic islets of a diabetic subject was made more than 100 years ago. Islet amyloidosis can affect less than 1% or up to 80% of islets in a diabetic individual. The occurrence of islet amyloid in non-diabetic subjects is low, less than 15% in elderly, apparently non-diabetic individuals, but is high in more than 90% of diabetic subjects postmortem. In 1987, two groups identified the constitutive protein in islet amyloid, denoting it Amylin or IAPP. As other amyloid-related diseases, the amyloid deposits in pancreatic islets were considered as the primary toxic agent and as a primary cause of pancreatic degeneration for many years.
In the last decade this dogma was challenged by several studies suggesting that soluble oligomers may be the primary toxic species as islet amyloid is also found in non-diabetic individuals, particularly with elderly population, and is not present in all islets in people with T2D. Homozygous transgenic mice of human IAPP (hIAPP) developed severe diabetes due to a high rate of β-cell apoptosis already at the age of 10 weeks. However, extracellular islet amyloid was not yet present in these mice during the rapid loss of β-cells from age 5-10 weeks. In obese hemizygous hIAPP mice that develop diabetes at approximately 20 weeks of age, extensive islet amyloid does accrue, but there is a poor correlation between the extent of islet amyloid and the frequency of β-cell apoptosis.
Porat, Y., et al., Biochemistry 42, 10971-10977, (2003) showed that the soluble structures of the hIAPP peptide interact and destabilize biological membrane. By showing that inhibition of IAPP fibrillation by rifampicin did not inhibit toxicity towards pancreatic cells, Meier et al. [Am. J. Physiol. Endocrinol. Metab. 291, E1317-1324, (2006)] proved that oligomers are probably the primary toxic epitope in T2D.
In spite of the extensive clinical importance of amyloid oligomers formation in T2D, the molecular mechanism that leads to the self-assembly and molecular recognition process is still not fully understood and soluble oligomers were never stabilized as distinctive entities.
U.S. Patent Application Publication No. 20090246191 teaches crosslinked prefibrillar aggregates of IAPP and crosslinked forms of Beta amyloid oligomers.
Porat et al., [Biochem, 2003, 42, 10971-10977] teaches pre-fibrillar structures of IAPP having a beta sheet secondary structure.